Stretch laminates are commonly used in the consumer-products industry. For example, stretch laminates are used in the manufacturing of disposable absorbent articles, such as disposable diapers. Conventional stretch laminates often comprise of at least two nonwoven materials having at least one elastic film sandwiched therebetween. In the manufacturing of such conventional laminates, the use of adhesive is often employed.
FIG. 1a shows a schematic of a conventional manufacturing process 1000 for the making of conventional stretch laminates. A first web of nonwoven material 10 is supplied in a direction as indicated by arrow 11. Adhesive 20 is applied to said first nonwoven 10 by way of an adhesive applicator 22. A second web of nonwoven material 12 is supplied in a direction as indicated by arrow 13. Adhesive 21 is applied to said second nonwoven 12 by way of an adhesive applicator 23. A web of elastic film 30 is supplied in a direction as indicated by arrow 31. These three webs of materials are sandwiched together between combining rolls 70, 72. Said combining rolls rotate in a direction as indicated by arrows 71, 73, respectively. Once these three webs of materials are sandwiched together, they are subsequently activated between activation rolls 80, 82. Said activation rolls rotate in a direction as indicated by arrows 81, 83, respectively. Activation of said webs by way of activation rolls 80, 82 is sometimes referred to as “ring rolling”. After said activation, the resulting product is a stretch laminate 99.
FIG. 1b shows the applicator adhesive 22 from that of FIG. 1a. Adhesive applicator 22 may comprise of a manifold 24, an adhesive inlet 25 and a slot 26. Referring now to FIG. 1c slot 26 may comprise of a backplate 27, shim 28 and a front plate 29. Referring now to FIG. 1d, an exploded view of slot 26 is shown. As can be seen, backplate 27 may comprise of a plurality of adhesive inlet ports 27a. Adhesive may be introduced into slot 26 through said adhesive inlet ports. Said adhesive may then exit through adhesive outlet port 27b, whereupon the adhesive will come into contact with shim 28. Shim 28 may consist of multiple regions including a closed portion 28c, an open portion 28o and a partitioned section 28f. The functionality of these various regions will be discussed later.
FIG. 1e shows the exemplary shim 28 from that of FIG. 1d. Further, an exemplary deposition of adhesive is shown having exited through shim 28. For instance, adhesive intended to be placed between said first and second nonwoven materials and also laterally outboard of elastic film 30 is identified as 20n. Additionally, an adhesive intended to be placed between said first and second nonwoven materials and also on the outboard edges of elastic film 30 is identified as 20t. Finally, an adhesive intended to be placed between said first and second nonwoven materials and also laterally positioned inboard the edges of elastic film 30 is identified as 20f. Referring now to FIG. 1f, a cross-sectional view of the adhesive deposition patterned from FIG. 1e is shown. As can be appreciated from this cross-sectional view, the adhesive within the region intended to be placed above or below elastic film 30 is discontinuous while the adhesive in the other regions is continuous. As is also depicted in this figure, and as experienced through conventional use, supplying adhesive in this manner (i.e. via a single source of adhesive supply) does not properly yield continuous regions of adhesive having varying and controllable amounts. The importance of such inadequacy within the prior art will be further examined later.
FIG. 1g shows the first web of nonwoven material 10 having regions of adhesive. For example, a full coverage of adhesive 20 is applied in the areas surrounding the subsequent placement of elastic film 30. In the areas which will be underneath the subsequent placement of elastic film 30, a partial coverage of adhesive 20f is applied. In this particular example, a series of parallel lines of adhesive is applied. Similar to the first web of nonwoven material 10, the second web of nonwoven material 12 also has regions of adhesive. For example, a full coverage of adhesive 21n is applied in the areas surrounding the subsequent placement of elastic film 30. In the areas which will be underneath the subsequent placement of elastic film 30, a partial coverage of adhesive 21f is applied. In this particular example, a series of parallel lines of adhesive is applied. As is also shown in this conventional embodiment, two webs of elastic film 30, are aligned with said parallel lines of adhesive 20f, 21f. Partial application of adhesive in this manner is important because these regions will be subjected to ring rolling as discussed above; therefore, these regions of material must be sufficiently elastic so as not to create pinholes. The areas of full coverage, 20n, 21n will not be significantly activated, rather these areas of full coverage provide for maximum adherence of first and second nonwoven materials.
FIG. 2a shows another exemplary slot 26 having a backplate 27, shim 28 and frontplate 29. Similar to that of the slot shown in FIG. 1d, backplate 27 has adhesive inlet ports 27a. However, within this particular example, shim 28 does not contain partitioned regions; rather shim 28 contains only open regions 27o and closed regions 28c. Referring now to FIG. 2b, the corresponding adhesive deposition for shim 28 of FIG. 2a is provided. As can be appreciated, said deposition of adhesive is continuous along the entire cross-section of adhesive (see FIG. 2c). And while shim 28 contains open regions 27o having varying heights, the resulting adhesive deposition (as shown in FIG. 2c) does not have complementary variations in amount which are controllable because of the inadequacies of supplying adhesive in the manner as shown (e.g., use of a single adhesive supply supplying adhesive via a single inlet). Referring now to FIG. 2d, a first web of nonwoven material 10 having regions of adhesive is shown. Within this particular example, a full coverage of adhesive is applied throughout, unlike the example in FIG. 1g. Similar to the first web of nonwoven material 10, the second web of nonwoven material 12 also has a full coverage of adhesive 20. Full coverage of adhesive in this manner presents several technical difficulties including pinholes during activation.
FIG. 3a illustrates a cross-sectional view of the conventional stretch laminate 99 from FIG. 1g. As can be seen, a first web of nonwoven material 10 is shown at the base of said laminate and a second web of nonwoven material 12 is shown at the top of said laminate. In this particular example, two elastic films 30 are shown in special relationship with each other and sandwiched between said webs of nonwoven material. A first plane of adhesive is shown between said first web of nonwoven material 10 and said elastic film 30. Within said first plane of adhesive are distinct regions of adhesive, namely, continuous application of adhesive 20n and discontinuous application of adhesive 20f. The continuous application of adhesive 20n is substantially located near the ends and outside of elastic film 30. The discontinuous application of adhesive 20f is substantially located between the ends of elastic film 30. Similarly, a second plane of adhesive is shown between said second web of nonwoven material 12 and said elastic film 30. Within said second plane of adhesive are distinct regions of adhesive, namely, continuous application of adhesive 21n and discontinuous application of adhesive 21f. The continuous application of adhesive 21n is substantially located near the ends and outside of elastic film 30. The discontinuous application of adhesive 21f is substantially located between the ends of elastic film 30.
FIG. 3b shows the cross-sectional view of FIG. 3a with particular emphasis on the continuous application of adhesive 20n, 21n. One of the primary purposes of application of adhesive within these regions is the proper lamination of first and second webs of nonwoven materials. As can be seen and appreciated, however, in the areas in which elastic film 30 is not present there exists a redundant supply of adhesive 20n, 21n. More importantly, it is often a problem of the prior art that this redundant supply of adhesive will penetrate the first and/or second webs of nonwoven materials thus causing performance and/or aesthetic issues. For this reason, the amount of adhesive applied in these first and second planes of adhesive is often kept below a fixed maximum value so as to minimize bleed through and above a fixed minimum value so as to provide sufficient adhesive for lamination.
FIG. 3c shows the cross-sectional view of FIG. 3a with particular emphasis on the continuous application of adhesive 20t, 21t within the areas identified with the letter “T”. These areas of adhesive, which are located at the ends of elastic film 30, are often referred to as tackdown areas. Because this area of adhesive serves the primary purpose of tacking down the elastic film 30 into place, a sufficient amount of adhesive must be supplied. Unlike the areas of adhesive outside of elastic film 30, these tack down areas gain the benefit of the presence of elastic film 30 such that bleeding of adhesive through first and second web of nonwoven material is not a major concern. Unfortunately, the designs of conventional stretch laminates and their respective manufacturing processes do not provide proper means for applying differing amounts of adhesive to address the competing interests of bleed through and sufficient tack down.
FIG. 3d shows the cross-sectional view of FIG. 3a with particular emphasis on the discontinuous application of adhesive 20f, 21f within the areas identified with the letter “F”. These areas of adhesive, which are located between the ends of elastic film 30 is applied in a discontinuous pattern so as to provide for sufficient elasticity of elastic film 30 during activation. Even though the adhesive applied in these areas is discontinuous, attempts to provide for sufficient tack down and lamination often results in too much adhesive being applied within these regions. Thus causing pinholes during activation.
FIG. 3e shows a schematic of an exemplary ring rolling process involving a first activation roll 80 having protruding teeth and a second activation roll 82 having protruding teeth, which mates those of said first activation roll. While in reality the teeth of first and second activation rolls 80, 82 are positioned in an engaging manner, this schematic shows said rules being separated so as to show the proper orientation and alignment of stretch laminate 99 in relationship to said rules. As can be seen and appreciated, the discontinuous application of adhesive 20f, 21f are significantly located between said teeth while the continuous application of adhesive 20n, 21n are not significantly located between said teeth. Such orientation and alignment is common throughout the industry.
FIG. 4a shows a cross-sectional view of another exemplary, conventional stretch laminate 99. In this particular example, the first and second plane of adhesive application 20n, 21n is entirely continuous. This conventional stretch laminate may be easier to manufacture, thus perhaps cheaper; however, the problems of pinholes during activation (see FIG. 4b) may be more prevalent. This type of conventional stretch laminate is often used in applications wherein material barrier properties are not critical.
What is needed is a stretch laminate having differing amounts of adhesive so as to properly be activated. The present invention describes such a product and method of making the same.